Berkley Heavy Weights--Sink Worm

I picked up a pack, on sale, at BPS last week. The package says new, and I've never seen them before. There are two styles: fat and regular; both are 5". I picked up the regular style in the Breen color.

These worms are heavier than the traditional Berkley worms, a bit stiffer too. They have the shape of the Fat Dover Crawler. I held one up to the light, no insert. Perhaps a tungsten like powder, similar to those plastic weights for inserting into tubes? Or just a denser plastic?

The package suggests rigging them wacky or unweighted Texas style. I picked them up with wacky in mind.

Anyone have any experience with these stinky suckers?